Position emission tomography (PET) is an imaging technology used for medical procedures and research. Scanning performed with a PET system can be used produce images of specimens, such as two-dimensional and three-dimensional images of organisms. PET imaging can be used to track the movement of matter through an organism.
Prior to PET imaging, a tracer may be injected into, ingested by, or otherwise inserted into a specimen. The tracer may be a radioactive contrast agent, such as 18F-fluorodeoxyglucose (FDG). FDG is a glucose analog that is internalized more rapidly by cancer cells than by normal cells. As the FDG travels through the specimen (e.g., the specimen's circulatory system), the FDG can be monitored by the PET scanner. In some embodiments, the FDG may travel to an area of interest in the specimen. For example, the FDG may adhere to or be taken up by cells of interest. The high level of radioactivity of the area of interest in comparison with other tissue can allow visualization of an area of interest as a PET image based on a PET scan. Various tracer types, such as RGD peptides, nitroimidazoles, Cu-ATSM, etc., may be selected for a range of imaging applications, such as identifying hypoxia in tissues, imaging organs, tracing the flow of blood or other compounds through an organism, etc.
After the tracer has entered the organism, a PET scanner can detect pairs of annihilation photons emitted by the tracer isotope. Typically, one or more pairs of PET detectors are used to detect pairs of emitted protons. A specimen may be positioned between two PET detectors.
As the tracer in the specimen decays, the isotope emits a positron. When the positron interacts with an electron, a pair of annihilation photons is produced, with the photons moving in opposite directions. The two photons can be detected by two PET detectors that are located across from each other with respect to the specimen. When the two photons reach crystals of the two PET detectors, the crystals can absorb the energy of the photons and emit the energy as light. One or more light detectors attached to a crystal can determine the position and time of arrival of the photon (i.e., an event) based on light emitted by the crystal. If two light detectors of the two PET detectors detect corresponding photon arrivals within a particular time frame, the photons may be determined to be a coincidence event (and therefore are highly likely to have originated from the same annihilation event). Alternative PET scanning systems may use solid state detectors and gas detectors in lieu of crystals for detecting photon arrivals.
Images may be constructed from the data acquired by the PET imaging system. For example, mathematical construction, e.g., maximum a posteriori (MAP) reconstruction, can be used to construct an image based on the distribution of activity detected by the PET detectors. The detectors may be configured to detect one or more of beta rays, gamma rays, and other high energy radiation.
Currently available PET scanners may be unable to image or suboptimal for imaging certain conditions and features, such as features that are small compared to spatial resolution of whole-body PET scanners. The size ranges of available PET scanners do not accommodate all potential imaging subjects of interest to researchers and health practitioners. PET scanners designed to have a fixed configuration may limit the applications for which PET scanning can be performed. Additionally, the structures of current PET scanners limit the settings in which PET scanners are operated.
Embodiments described herein address these and other problems, individually and collectively.